The present invention is an improved gravure press for use in making multicolor proofs. The plate and paper registration are manual while the printing functions including cleaning the plate are automatically regulated. The improved gravure press includes a controlled ink distribution system and a cleaning unit for washing the plate after printing is completed.
The gravure system for printing is well-known in the art. The primary characteristic of the gravure method of printing is the clarity and sharpness of the reproduction. For this reason, the gravure method is used in the printing of multicolor material particularly when a pictorial illustration or design representation is present. Before the plates used to produce a multicolor copy are placed on a production type of press for large volume, it is common practice to generate several proof sheets of the copy. The proof sheets are examined for errors and artistic layout so that any errors or inconsistencies in the plates may be removed before a large quantity of inaccurate material is produced and unnecessary expense incurred.
Gravure multicolor proof presses are designed for low quantity production. The previously known gravure proof presses are predominantly hand operated. In the operation of known gravure flat bed proof presses, the operator will manually register the printing plate and align the paper on an impression cylinder. The first color of ink is applied by hand, commonly from a plastic deformable container, across one edge of the plate. A doctor blade is then manually used to spread the ink across the plate. The ink theoretically settles only in the wells or grooves below the planar surface of the printing plate. The impression or printing cylinder containing the paper is then moved by hand across the inked plate to obtain a copy with the first color of ink.
It is common to produce several sheets of copy in the same color ink before the plate is changed to repeat the printing operation with a different printing plate and a different color ink. However, the printing plate must be thoroughly cleaned before producing another proof sheet of the same color. The cleaning operation is critical and essential for the removal of all excess or dried ink, particularly within the wells or grooves in the plate. If the plate is not cleaned or if it is improperly cleaned, subsequent proof sheets will contain inconsistencies especially in plate well areas where dried ink remains and the new ink is precluded from properly settling. The plate well areas in which the new ink does not settle do not produce an image on a subsequently pulled proof sheet. The cleaning operation is a manual procedure which includes the hand scrubbing of the plate on the press bed and the subsequent removal of the cleaning solution and diluted ink. It should be apparent that while described for a flat bed press, similar operations are necessary for a rotogravure press. Of course, the cleaning operation is repeated after the printing of each proof sheet for each color of ink needed. It is common for the completed proof to use four different colors of ink and correspondingly require four different printing plates, but it should be appreciated that any number of ink colors and plates more or less than four can be used following the same procedure.
There are numerous disadvantages of the known gravure proof presses. The time involved in the manual printing operation and clean up is extensive and the consequent cost of the finished proof is exorbitant. However, more important than the practical considerations of time and expense, the known gravure proof presses neither provide high quality proofs nor consistently uniform quality proofs. These latter disadvantages stem from the predominantly manual operation and its lack of uniform repeatability.
A major difficulty of manual operation is the application of ink to the print plate. Since the operator manually applies the ink, the quantity of ink necessarily varies for each application and the location of the placement of the ink changes. Since ink, especially printing ink, is quick drying in air, the quantity of ink applied, usually in an elongated bead along one edge of the plate, affects the ink's drying time parameter. Furthermore, the time lapse between ink application and manually spreading the ink with the doctor blade varies substantially between different applications. Consequently the degree of drying of the ink at the moment of doctor blade spreading is different and this affects the ink's spreadability characteristic. This time interval is erratic in manual operation and the uniformity and repeatability of the application and spreading process are uncontrollable.
Another problem area involves the pressure applied to the doctor blade during the spreading of the ink. Since the operation is manual, the applied pressure fluctuates between successive operations. This results in uneven settling of the ink into the print plate wells or noncomplete removal of excess ink from the plate surface. These circumstances result in streaks of ink on the proof sheet or a variable density of the reproduced lines on the proof sheet.
Yet another difficulty in known gravure proof press operation is the inconsistent movement of the print cylinder across the inked plate. If the speed of movement is not uniform, the paper absorbs different amounts of ink dependent upon the length of time that the paper remains in contact with the inked plate. The amount of ink absorbed from the plate determines the sharpness of color of the produced image on the proof sheet. The manual operation renders speed of movement and hence sharpness of color unrepeatable.
A further disadvantage of known gravure presses is the manual cleaning or washing necessary after each printing step or pull. The quality of manual cleaning is variable and uncertain. In addition to being time-consuming and messy, the manual cleaning leaves dried ink or solvent on the plate. Any foreign material on the plate during the printing step appears in some undesirable manner on the proof sheet. The foreign matter results in a streak of ink if it remains on the planar surface of the print plate. If dried ink remains within the printing plate wells, a subsequent application of ink is unable to settle in the appropriate well and that uninked area does not produce an image on the pulled proof sheet. The manual cleaning of the printing plate results in poor quality proofs.
These and other disadvantages of known gravure multicolor proof printing make it a costly and time-consuming operation. In addition, the quality of the completed multicolor proof sheet is erratic and the repeatability of the process inconsistent.